This invention relates generally to dry flexible glue compositions and to a method for preparing the same. In particular, the invention relates to flexible glue compositions containing synthetic hydrous alkaline earth metal silicates or synthetic silicates.
The adhesive industry defines a flexible glue as one whose film remains flexible for long periods of time under conditions of average use. Animal glue, which is the protein polymer derived from animal hides and bones is made flexible by the addition of a plasticizer.
Over the past decades, glycerine has proven to be the best plasticizer for animal glue and is the standard when comparing film flexibility and retention of flexibility over extended periods of time. Depending upon the degree of flexibility desired the amount of glycerine may vary from 30 to 125% of the glue.
For economic or performance reasons, other liquid plasticizers may be employed or partially substituted for glycerine. These materials are various polyols, such as glycols, dextrose, corn syrup, sorbitol and the like. Flexible glue formulae may also contain inorganic salts, clays, pigments, solvents, surfactants, odorants, defoamers, etc. depending upon the end use or economic requirements.
Flexible glue is generally prepared by dispersing the dry animal glue in cold water, allowing the granules to swell raising the temperature to 130.degree.-160.degree. F., dissolving the glue and then adding the plasticizer and other ingredients. After adjusting to the proper specifications, the flexible glue is drawn off in suitable containers, and shipped after gelling, in the form of flexible cakes.
Some years ago the adhesive industry introduced so-called dehydrated flexible glue compositions. These are dry blends of ground animal glue; solid plasticizers such as sugar, dextrose, corn syrup solids, etc; inorganic salts, such as magnesium sulfate, sodium chloride, etc; fillers; and small additions of defoamer and odorants. The primary advantages of such products are in lower freight costs, longer shelf life of the product and flexibility in controlling solids on application. The great disadvantage is the inability to attain flexibility of the glue film equivalent to that obtained with glycerine and, therefore, these dehydrated flexible glues have limited application.